Superabrasive compacts are utilized for a variety of applications and in a corresponding variety of mechanical systems. Such superabrasive compacts may be known in the art, for example, as inserts, buttons, machining tools, wear elements, or bearing elements and may be conventionally manufactured by forming a superabrasive layer on the end of a substrate (e.g., a sintered or cemented tungsten carbide substrate). As an example, polycrystalline diamond, or other suitable superabrasive material, such as cubic boron nitride, may be sintered onto the surface of a cemented carbide substrate under an ultra-high pressure and ultra-high temperature (“HPHT”) process to form a superabrasive compact, as described in greater detail below. Polycrystalline diamond elements are used in drilling tools (e.g., inserts, cutting elements, gage trimmers, etc.), machining equipment, bearing apparatuses, wire drawing machinery, and in other mechanical systems. For instance, polycrystalline diamond compacts (PDCs) have found utility as cutting elements in drill bits (e.g., roller cone drill bits and fixed cutter drill bits).
Such PDCs conventionally include a diamond layer or table formed by a sintering process employing HPHT conditions that causes the diamond table to become bonded or affixed to a substrate (such as cemented tungsten carbide substrate), as described in greater detail below. Optionally, the substrate may be brazed or otherwise joined to an attachment member such as a stud or to a cylindrical backing, if desired. Generally, a rotary drill bit may include a plurality of polycrystalline abrasive cutting elements affixed to the drill bit body. Each PDC may be employed as a subterranean cutting element mounted to a drill bit either by press-fitting, brazing, or otherwise coupling a stud to a recess defined by the drill bit, or by brazing the cutting element directly into a preformed pocket, socket, or other receptacle formed in the subterranean drill bit. In one example, cutter pockets may be formed in the face of a matrix-type bit comprising tungsten carbide particles that are infiltrated or cast with a binder (e.g., a copper-based binder), as known in the art. Such subterranean drill bits are typically used for rock drilling and for other operations which require high abrasion resistance or wear resistance.
A PDC is conventionally fabricated by placing a cemented carbide substrate into a container or cartridge with a layer of diamond crystals or grains positioned adjacent one surface of a substrate. A number of such cartridges may be typically loaded into an ultra-high pressure press. The substrates and adjacent diamond crystal layers are then sintered under HPHT conditions. The HPHT conditions cause the diamond crystals or grains to bond to one another to form polycrystalline diamond. In addition, as known in the art, a catalyst may be employed for facilitating formation of polycrystalline diamond. In one example, a so-called “solvent catalyst” may be employed for facilitating the formation of polycrystalline diamond. For example, cobalt, nickel, and iron are among examples of solvent catalysts for forming polycrystalline diamond. In one configuration, during sintering, a solvent catalyst comprising the substrate body (e.g., cobalt from a cobalt-cemented tungsten carbide substrate) becomes liquid and sweeps from the region adjacent to the diamond powder and into the diamond grains. Of course, a solvent catalyst may be mixed with the diamond powder prior to sintering, if desired. Also, as known in the art, such a solvent catalyst may dissolve carbon. Such carbon may be dissolved from the diamond grains or portions of the diamond grains that graphitize due to the high temperatures of sintering. When the solvent catalyst is cooled, the carbon held in solution may precipitate or otherwise be expelled from the solvent catalyst and may facilitate formation of diamond bonds between abutting or adjacent diamond grains. Thus, diamond grains become mutually bonded to form a polycrystalline diamond table upon the substrate. A conventional process for forming polycrystalline diamond cutters is disclosed in U.S. Pat. No. 3,745,623 to Wentorf, Jr. et al., the disclosure of which is incorporated herein, in its entirety, by this reference.
Solvent catalyst in the polycrystalline diamond may be detrimental. For instance, because the solvent catalyst exhibits a much higher thermal expansion coefficient than the diamond structure, the presence of such solvent catalyst within the diamond structure is believed to be a factor leading to premature thermal mechanical damage. Accordingly, as the polycrystalline diamond reaches temperatures exceeding 400° Celsius, the differences in thermal expansion coefficients between the diamond and the solvent catalyst may cause diamond bonds to fail. Of course, as the temperature increases, such thermal mechanical damage may be increased. In addition, as the temperature of the polycrystalline diamond layer approaches 750° Celsius, a different damage mechanism may initiate. More specifically, the solvent catalyst may interact with the diamond to cause graphitization of the diamond. Such graphitization is believed to contribute to or cause mechanical damage within the polycrystalline diamond. This phenomenon may be termed “back conversion,” meaning conversion of diamond to graphite. Such conversion from diamond to graphite may cause dramatic loss of wear resistance in a polycrystalline diamond compact and may rapidly lead to insert failure. Accordingly, as known in the art, the solvent catalyst in the polycrystalline diamond layer may be at least partially removed from the polycrystalline diamond. For instance, the solvent catalyst may be at least partially removed from the polycrystalline diamond by acid leaching. Optionally, another material may replace the solvent catalyst that has been at least partially removed from the polycrystalline diamond.
Accordingly, a superabrasive volume may include at least two regions with differing constituents. Thus, it may be advantageous to determine or perceive different regions of a superabrasive volume. For instance, such perception may allow for monitoring of (i.e., quality control) relative to superabrasive apparatus manufacturing and processing methods. Thus, it would be advantageous to provide methods and systems for evaluating (e.g., nondestructively) different regions of a superabrasive volume.